The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A selective catalytic reduction (SCR) catalyst may be used to reduce emissions in an engine. In an SCR process, nitrogen oxide (NOx) reacts with a reductant that is injected by a dosing system into an exhaust stream. The reductant is adsorbed onto the SCR catalyst. The injected dosing agent (e.g., urea) decomposes to form ammonia (NH3). The NH3 is the reductant utilized to react with the NOx, reducing it to nitrogen (N2) and water (H2O).
The SCR process typically requires relatively high exhaust temperatures (e.g., greater than 200° C.). At cold start and at low load operating conditions, engines may generate exhaust with cool exhaust temperatures (e.g., below 200° C.). Accordingly, during a cold start phase the highest temperature of the SCR catalyst may be lower than the temperature required to make the SCR catalyst active in reducing NOx emission.